Friedel-Crafts acylation has been known to be a basic and useful method of preparing aromatic ketones. For Friedel-Crafts acylation, a catalytic amount of Lewis acid is used, while in acylation, more than a stoichiometric amount of Lewis acid such as AlCl3 is normally required. However, environmental problems that needs to be considered are evoked by the large amount of aluminum residue derived from AlCl3, especially in industrial-scale processes. For solving such problems, several types of excellent catalysts have been developed, and catalytic acylation of active benzenes such as anisole, xylene and toluene have been realized. However, the realization of catalytic Friedel-Crafts acylation of benzene and inactive benzenes such as chlorobenzene has still been difficult. Under these circumstances, in recent years, Dubac et al. and the present inventor's group have found and reported in the following literature that Bi(OTf)3, Hf(OTf)4 and the like are effective catalysts for the Friedel-Crafts acylation of benzene and inactive benzenes.
TABLE 1(a) Desmurs, J. R.; Labrouillere, M.; Roux, C. L.; Gaspard, H.;Laporterie, A.; Dubac, J. Tetrahedron Lett. 1997, 38, 8871.(b) Repichet, S.: Roux, C. L.; Dubac, J.; Desmurs, J. -R. Eur.J. Org. Chem. 1998, 2743.
TABLE 2(a) Hachiya, I.; Moriwaki, M.; Kobayashi, S. Tetrahedron Lett. 1995, 36,409. (b) Hachiya, I.; Moriwaki, M.; Kobayashi, S. Bull. Chem. Soc. Jpn.1995, 68, 2053. (c) Kobayashi, S.; Iwamoto, S. Tetrahedron Lett.1998, 39, 4697.
Further, quite recently, the present inventors have found that gallium catalysts, especially gallium tri(perfluoroalkane sulfonate), exhibits the highest activity in Friedel-Crafts acylation (Matsuo, J.; Odashima, K.; Kobayashi, S. Synlett 2000, 403).
Meanwhile, it has been found that ketoaniline structures are important in physiologically active compounds and fine chemicals, and the realization of means to efficiently synthesize these compounds while controlling their structures, has become an important subject. However, while the Friedel-Crafts acylation of aniline derivatives is a simple and clear method of introducing an acyl group into a benzene ring, and while a novel Friedel-Crafts acylation method for the synthesis of aromatic ketones has been realized by the present inventor's group as stated above, actual examples of a catalytic reaction have not yet been reported.
Accordingly, the present invention aims to provide, under the foregoing circumstances, a novel Friedel-Crafts acylation method that enables the synthesis of ketoaniline derivatives useful as physiologically active compounds or intermediates thereof, in high reaction yield through catalytic reaction.